In the past, suspension systems in general have been used for many applications, including cushioning impacts, vibrations or other disturbances experienced by vehicles and machinery. Typical applications, for example, include the use of suspension systems in bicycles and motorcycles.
For example, bicycles have been developed with suspension systems for cushioning impacts or vibrations experienced by the rider when the bicycle contacts bumps, ruts, rocks, pot holes or other obstacles and road variations. Typically, such bicycle suspension systems have been configured for use in the front or rear bicycle fork, in the head tube that connects the front fork to the bicycle frame and handlebars, in the seat post, and in conjunction with a rear wheel swing-arm assembly, among other locations.
It has become increasingly popular to locate bicycle suspension systems within bicycle forks. Bicycle suspension forks comprise at least one fork leg or strut, and usually comprise two such struts, each strut including inner and outer telescoping fork members or tubes. Bicycle fork suspension systems have often included spring devices such as coil springs, elastomer springs, arcuate spring discs, leaf springs, gas springs such as air springs, among other types of springs used for nominally biasing the fork tubes apart from one another and for absorbing compression forces applied to the forks as a result of impacts and vibrations experienced during operation of the bicycle. Using spring devices in this way permits the fork members to compress in response to an impact or other force input, and expand or rebound once the force is removed, so that the inner and outer fork members or tubes return to their original spaced apart positions relative to each other. Such bicycle suspension systems have also included spring devices in combination with damping devices such as hydraulic damping or friction damping mechanisms, which absorb some of the energy imparted to the bicycle by impacts or other force inputs causing compression or rebound of the fork members, thereby resisting movement of the fork members relative to each other.
One problem associated with prior suspension systems, and particularly with vehicle suspension systems such as those incorporated into bicycle suspension forks, is that they have been unnecessarily heavy. For example, the weight of a bicycle fork affects the handling of the bicycle, and adds to the overall weight of the bicycle, which the rider must work to propel and control. Reducing weight is therefore of great concern to all bicycle riders, and particularly to those involved in racing applications, where a reduction in weight offers an important competitive advantage. Accordingly, there is a need for a suspension system, and particularly for a bicycle suspension fork, that is designed to be lightweight.
In the past, weight savings have been achieved in suspension systems such as bicycle suspension forks by using a gas spring as the spring device, instead of heavier spring devices such as metal coil springs and the like. The resulting gas-sprung designs have suffered from disadvantages, however, including limited tunability and, therefore, an inability to accommodate a wide variety of rider preferences. Consequently, there is a need for a gas-sprung suspension device, and particularly a gas-sprung bicycle suspension fork, that is designed to be fully tunable.
One adjustment feature that has been incorporated into gas-sprung suspension systems such as suspension forks is the ability to increase or decrease the gas pressure in the suspension system. In bicycle suspension forks as in other suspension systems, one problem associated with this adjustment feature is that an increase or decrease in the fork gas pressure results in a corresponding increase or decrease in the spring force, and, accordingly, in the compressive force required to be applied to the fork before the inner and outer fork tubes will begin to compress in response to a bump or other force input (this force is commonly known as the "crack force"). Thus, depending upon the gas pressure in the gas spring, the suspension system may be undesirably stiff, and adequately responsive only to large inputs.
In gas-sprung bicycle suspension forks, for example, if the crack force is too large for a given rider, the fork will act much like a rigid, unsuspended fork in response to relatively small force inputs. If the crack force is too small, the fork tubes will compress easily and may sag extensively in response to the rider's weight, thus reducing their available compressive travel during use. Neither condition is desirable, and the wide range of potential rider weights and preferences makes the use of a pre-set or inadequately adjustable crack force problematic. Thus, there is a need for a gas-sprung suspension system, and particularly for a gas-sprung suspension bicycle fork, that is designed to have an improved adjustment feature for adjusting the crack force of the fork.
In gas-sprung suspensions, compression of the telescoping members of the suspension system compresses the gas. Due to the nonlinear spring rate of gases ("spring rate" may be defined as the amount of force required to compress or expand the suspension system a given distance) the spring force generated by the gas chamber will increase dramatically toward the end of the telescoping members' travel. Delaying the onset of this ramp-up in gas spring force will result in a softer suspension, whereas hastening the onset of the force ramp-up will result in a stiffer suspension. To accommodate a variety of weights to be suspended, and, where vehicles such as bicycles are concerned, to accommodate a broad range of user preferences, it is desirable to be able to adjust the spring force ramp-up location. Thus, there is a need for a gas-sprung suspension system, and particularly for a gas-sprung suspension bicycle fork, that is designed to have an improved adjustment feature for adjusting the onset of the ramp-up in spring force during compression of the suspension system.
In addition, previous suspension system designs, and bicycle suspension fork designs in particular, typically have been limited to a single spring rate during both the low and high velocity compression or rebound regimes of the suspension system. This is true for gas-sprung suspension systems as well as for suspension systems using spring devices other than gas. Generally, a lesser spring rate is desirable for small bumps and other low-velocity inputs in order to achieve a supple suspension, whereas a relatively greater spring rate is desirable for high-velocity inputs in order to avoid over-reactive responses by the suspension system.
This principle can be readily seen in bicycle applications, where a lesser spring rate results in a more comfortable ride over small bumps and the like, and a relatively greater spring rate provides greater control in response to large bumps and sudden impacts. Thus, there is a need for a suspension system, and particularly for a bicycle suspension system, having a spring rate that varies based upon the speed or frequency of the compression or rebound of the suspension system.
As previously indicated, in many applications, and particularly in bicycling and bicycle racing applications, the desirability of being able to adjust the performance characteristics of the suspension system is significant. Accordingly, there is a need for a suspension system, and particularly for a bicycle suspension system, in which the spring rate is frequency-sensitive, and in which such speed-sensitivity of the spring rate is adjustable.
In addition, it is desirable to have a suspension system comprising each of the previously described features, resulting in a suspension system that is suited for suspension applications in general, and particularly for bicycle suspension applications, and that is active and tunable for a wide variety of riding preferences.
In order to provide greater control of the compression and/or rebound characteristics of the suspension system, it is also desirable for a suspension system to have each of the previously described features in combination with hydraulic damping.
Accordingly, one object of the present invention is to provide a suspension system, and particularly a bicycle suspension fork, that is designed to be lightweight.
Another object is to provide a gas-sprung suspension device, and particularly a gas-sprung bicycle suspension fork, that is designed to be fully tunable.
A further object of the invention is to provide a gas-sprung suspension system, and particularly a gas-sprung suspension bicycle fork, that is designed to have an improved adjustment feature for adjusting the crack force of the fork.
Yet another object is to provide a gas-sprung suspension system, and particularly a gas-sprung suspension bicycle fork, that is designed to have an improved adjustment feature for adjusting the onset of the ramp-up in spring force during compression of the suspension system.
Still a further object of the invention is to provide a suspension system, and particularly a bicycle suspension system, having a spring rate that varies based upon the speed or frequency of the compression or rebound of the suspension system.
Another object is to provide a suspension system, and particularly a bicycle suspension system, in which the spring rate is frequency-sensitive, and in which such speed-sensitivity of the spring rate is adjustable.
Yet another object is to provide a lightweight, fully tunable suspension system having an improved adjustment feature for adjusting the crack force of the fork, an improved adjustment feature for adjusting the onset of the ramp-up in spring force during compression of the suspension system, and a spring rate that varies based upon the speed or frequency of the compression or rebound of the suspension system, the speed-sensitivity of which can be adjusted, resulting in a suspension system that is suited for suspension applications in general, and particularly for bicycle suspension applications, and that is active and tunable for a wide variety of riding preferences.